1. Field of the Invention
The present invention relates to an apparatus for moulding and vulcanisation of tyres for vehicle wheels.
2. Description of the Related Art
In a tyre production cycle it is provided that, subsequently to a building process during which a green tyre is obtained through assembling of the different tyre components, a moulding and vulcanisation process be carried, said process aiming at stabilising the tyre structure according to a desired geometric conformation usually characterised by a particular tread pattern.
To this end, the tyre is introduced into a vulcanisation apparatus of the type disclosed, for example, in U.S. Pat. No. 5,234,326 in the name of the same Applicant.
This apparatus comprises a pair of plates adapted to be moved close to each other and designed to operate on the tyre bead and sidewalls, and at least one crown of circumferentially distributed mould sectors radially movable close to each other to operate at the tyre tread band. In more detail, the plates and sectors are mutually movable between an open condition at which they are spaced apart to enable loading of the tyres under manufacture and a closed condition at which they define a moulding cavity having a geometric configuration matching the outer surfaces of the tyre to be obtained. For the moulding and vulcanisation operation, a vulcanisation bladder of elastomeric material filled with steam and/or other fluid at high temperature and pressure and placed inside the tyre enclosed in the moulding cavity, is provided to be inflated. In this way, the tyre is pushed against the inner walls of the moulding cavity and stabilised into the geometric conformation imposed on it, following cross-linking.
The moulding sectors, supported by appropriate sector carriers, are brought to the closed or open condition by a vulcanisation press that, acting by means of mechanical connections on the sector carriers, operates sliding of the latter on suitable guide elements and, as a result, movement of the mould sectors.
The Applicant has ascertained that the moulding and vulcanisation apparatuses as above described have some problems.
In fact, it was observed that during shifting of the mould sectors, above all towards the closed condition, sliding of the sector carriers on the respective guide elements, due to the weight of the sector carriers themselves, may involve jamming and uneven wear of the guide elements. In fact, the sector carriers by the action of their weight, tend to separate from the guide elements generating a relative slight rubbing between said parts.
The uneven wear of the guide elements may give rise to wrong positioning of the sector carriers in the closed condition and, as a result, of the mould sectors. Thus geometric and/or structural faults such as burr and step formation, can occur on the tyre tread band.